This invention relates to an overload protective system for a fork lift truck which is responsive to an excessive tilting moment acting on the truck, as a result of a load on a carriage elevated on a tilted mast, to inhibit further raising of the carriage of further forward tilting of the mast, thereby preventing the operator from increasing the danger of overturning the truck during material handling operations.
Overload protection systems for a fork lift truck are known of the type disclosed in U.S. Pat. No. 4,003,487 in the name of Terry R. Downing having the same assignee as this invention which monitors the overturning, or tilting moment acting on the truck and generates an overload, or trip signal when the overturning moment is excessive and, in response to the trip signal, disables the mast tilting motor and the carriage elevating motor from shifting the carriage in a direction which would increase the danger of overturning the truck. However, such known overload protective systems may include a complex electronic circuit with many electronic components which can fail and thus prevent the protective circuit from responding properly to the excessive overload, and consequently it is possible to raise the carriage further on an already overloaded truck which has a failed component in the protective system and to also tilt the mast thereof further forward, thereby increasing the danger of overturning the truck which is already overloaded.